During cardiac surgery, it is often necessary to introduce a cannula into an artery or other blood vessel. For example, an arterial cannula is typically introduced into the aorta to deliver blood from a bypass-oxygenator system. Such a cannula generally includes a proximal end for receiving blood from a bypass-oxygenator machine, a distal end for entry into an artery and a lumen extending between the proximal and distal ends.
One concern with such procedures is that calcified plaque or other embolic material may be dislodged, particularly when clamping or unclamping arteries such as the aorta. See Barbut et al., "Cerebral Emboli Detected During Bypass Surgery Are Associated With Clamp Removal," Stroke, 25(12):2398-2402 (1994), which is incorporated herein by reference in its entirety. Such embolic material may travel downstream, possibly becoming lodged in another portion of the blood vessel or possibly reaching a vital organ, such as the brain, where the material can cause substantial injury to the patient.
For this reason, some arterial cannulas may include a blood filter device attached directly to them. For example, an expandable filter device may be mounted on the distal end of a cannula, allowing the filter to capture any loose embolic material once the cannula is introduced into the vessel. Generally, such devices include an expandable frame, such as an inflation seal or an umbrella frame, and a filter mesh attached to the frame, the mesh being adapted to capture embolic material of a predetermined minimum size. The frame may be attached externally to the distal end, or alternatively, it may be retractably deployed from a lumen within the cannula.
The use of a cannula with such a filter device, however, may not be as effective as desired. For example, because the filter is generally attached to the distal end of the cannula, the filter may be exposed within the vessel for the entire duration of the procedure, sometimes several hours. Because of the length of time of most cardiac procedures, the filter mesh may eventually become clogged due to thrombus formation or buildup of embolic material, preventing the device from effectively capturing additional material and/or possibly impairing blood flow through the filter. If the filter is retractable, it may be closed within the vessel when it becomes clogged, but this prevents capture of embolic material throughout the remainder of the procedure.
Accordingly, there is a need for a filter device for use with an arterial cannula or other hollow vessel insertion device, such as an introducer, that minimizes the exposure of the filter within a blood vessel, thereby reducing the risk of clogging the filter mesh. Certain types of self-expanding modular filter devices have been described in U.S. Ser. No. 08/853,165, filed May 8, 1997, which is incorporated herein by reference in its entirety. However, there is a need for a modular filter apparatus with a filter that can be adjusted to fit various sizes of vessels. The exterior of such a device should optimally conform to the size and shape of the inner lumen of the vessel through which the emboli may pass to reduce the possibility of emboli escape around the exterior of the filter. The size of such a filter should either be self-adjusting or adapted to external operation to adjust the size to fit the vessel in which the filter resides. Further, there is a need for associated devices such as vessel sizing tools, expandable obturators, cannula liners and blood filtering system indexing/locking devices to assist in the use of the blood filtering system.